RFID tag limiter

ABSTRACT

A Radio Frequency Identification (RFID) tag is disclosed. The RFID tag includes an antenna port to receive an input AC signal and a hybrid limiter including a clamping device configured to limit a voltage of the input AC signal to a preconfigured limit. The hybrid limiter is configured to provide a stable ground reference for the clamping device.

BACKGROUND

Radio Frequency Identification (RFID) refers to a wireless systemcomprised of two components: tags and readers. The reader is a devicethat has one or more antennas that emit radio waves and receive signalsback from the RFID tag. Tags, which use radio waves to communicate theiridentity and other information to nearby readers, can be passive oractive. Passive RFID tags are powered by the reader and do not have abattery. Active RFID tags are powered by batteries. Near FieldCommunication (NFC) is a wireless communication technology that actsover short distances for two-way communication. The use of NFC tags isgrowing in several markets, including the medical, consumer, retail,industrial, automotive, and smart grid markets. NFC is a type of RFIDtechnology. Due to internal or external factors such as distance fromthe other device or tag, nearby objects, etc. the tag needs to be tunedto balance the impedance to optimize the received signal strength beforea data read cycle starts.

SUMMARY

This Summary is provided to introduce a selection of concepts in asimplified form that are further described below in the DetailedDescription. This Summary is not intended to identify key features oressential features of the claimed subject matter, nor is it intended tobe used to limit the scope of the claimed subject matter.

In one embodiment, a Radio Frequency Identification (RFID) tag isdisclosed. The RFID tag includes an antenna port to receive an input ACsignal and a hybrid limiter including a clamping device configured tolimit the voltage of the input AC signal to a preconfigured limit. Thehybrid limiter is configured to provide a stable ground reference forthe clamping device. In some examples, the RFID tag includes aninterface port and a ground port.

In some examples, the clamping device includes a first transistor and asecond transistor coupled between terminals of the antenna port. Thefirst transistor and the second transistor are of type NMOS. The RFIDtag further includes a third transistor coupled between a first terminalof the antenna port and a ground. The third transistor is smaller inphysical size than the first transistor. The RFID tag includes a fourthtransistor coupled between a second terminal of the antenna port and aground. The fourth transistor is smaller in physical size than thesecond transistor. The gate of the first transistor and the gate of thethird transistor are driven by a same gate voltage (V_(G)). The gate ofthe first transistor and gate of the fourth transistor are driven by thesame gate voltage (V_(G)) that may be derived from the signal at theantenna port using a rectifier circuit. In some examples, a groundswitch may be used to implement the ground reference.

In another embodiment, a tamper detection system is disclosed. Thetamper detection system includes a RFID tag, an interface port and aground port. The RFID tag includes an antenna port to receive an inputAC signal, and a hybrid limiter including a clamping device configuredto limit the voltage of the input AC signal to a preconfigured limit.The hybrid limiter is configured to provide a stable ground referencefor the clamping device. In some examples, the RFID tag is configured todetect tampering by sensing ground at the interface port. The RFID tagis configured to transmit an indication of the tampering to an externalreader when no ground is sensed at the interface port. The RFID tag mayinclude a control logic configured to sense the ground at the interfaceport and to transmit the indication to the external reader via theantenna coupled with the antenna port. The hybrid limiter includes afirst transistor and a second transistor to provide a voltage clamp anda third transistor and a fourth transistor to provide a ground referencefor the voltage clamp.

BRIEF DESCRIPTION OF THE DRAWINGS

So that the manner in which the above recited features of the presentinvention can be understood in detail, a more particular description ofthe invention, briefly summarized above, may be had by reference toembodiments, some of which are illustrated in the appended drawings. Itis to be noted, however, that the appended drawings illustrate onlytypical embodiments of this invention and are therefore not to beconsidered limiting of its scope, for the invention may admit to otherequally effective embodiments. Advantages of the subject matter claimedwill become apparent to those skilled in the art upon reading thisdescription in conjunction with the accompanying drawings, in which likereference numerals have been used to designate like elements, and inwhich:

FIG. 1 shows a block diagram of a RFID tag in accordance with one ormore embodiments of the present disclosure;

FIG. 2 depicts an hybrid limiter circuit used in the RFID tag inaccordance with one or more embodiments of the present disclosure; and

FIG. 3 shows a tamper protection system using the RFID tag in accordancewith one or more embodiments of the present disclosure.

Note that figures are not drawn to scale. Not all components of the RFIDtag are shown. The omitted components are known to a person skilled inthe art.

DETAILED DESCRIPTION

Many well-known manufacturing steps, components, and connectors havebeen omitted or not described in details in the description so as not toobfuscate the present disclosure.

It will be readily understood that the components of the embodiments asgenerally described herein and illustrated in the appended figures couldbe arranged and designed in a wide variety of different configurations.Thus, the following more detailed description of various embodiments, asrepresented in the figures, is not intended to limit the scope of thepresent disclosure, but is merely representative of various embodiments.While the various aspects of the embodiments are presented in drawings,the drawings are not necessarily drawn to scale unless specificallyindicated.

The present invention may be embodied in other specific forms withoutdeparting from its spirit or essential characteristics. The describedembodiments are to be considered in all respects only as illustrativeand not restrictive. The scope of the invention is, therefore, indicatedby the appended claims rather than by this detailed description. Allchanges which come within the meaning and range of equivalency of theclaims are to be embraced within their scope.

Reference throughout this specification to features, advantages, orsimilar language does not imply that all of the features and advantagesthat may be realized with the present invention should be or are in anysingle embodiment of the invention. Rather, language referring to thefeatures and advantages is understood to mean that a specific feature,advantage, or characteristic described in connection with an embodimentis included in at least one embodiment of the present invention. Thus,discussions of the features and advantages, and similar language,throughout this specification may, but do not necessarily, refer to thesame embodiment.

Furthermore, the described features, advantages, and characteristics ofthe invention may be combined in any suitable manner in one or moreembodiments. One skilled in the relevant art will recognize, in light ofthe description herein, that the invention can be practiced without oneor more of the specific features or advantages of a particularembodiment. In other instances, additional features and advantages maybe recognized in certain embodiments that may not be present in allembodiments of the invention.

Reference throughout this specification to “one embodiment”, “anembodiment”, “one example”, or similar language means that a particularfeature, structure, or characteristic described in connection with theindicated embodiment is included in at least one embodiment of thepresent invention. Thus, the phrases “in one embodiment”, “in anembodiment”, and similar language throughout this specification may, butdo not necessarily, all refer to the same embodiment.

RFID tags can store a range of information from one serial number toseveral pages of data. RFID tags can be mobile so that they can becarried by hand, or they can be mounted on a post or overhead. RFIDsystems can also be built into the architecture of a cabinet, room, orbuilding. NFC is a technology based on RFID technology. NFC technologycan be used to provide peer-to-peer communication or one waycommunication. When two NFC enabled devices are very close to eachother, about 4 cm or less, they can communicate with each other usingthe radio waves. Of the two devices communicating using NFC, at least ofthem has to be an active device (powered). In many cases, this would bea smartphone, tablet, security pad, or a payment terminal. The otherdevice can be either active or passive (unpowered). Using NFC, twodevices can be set up in less than one-tenth of a second.

In an active peer-to-peer (P2P) mode, two active devices create awireless communication channel between them. The active device, with anexternal power supply, can power the passive device with theelectromagnetic field coming from the active device. U.S. Pat. No.9,997,928 entitled “self-tuning resonant power transfer systems” byPetersen describes tuning a wireless power transfer system, which isincorporated herein by reference. U.S. Pat. No. 8,836,512 entitled “Selftuning RFID” by Shanks describes the self-tuning of RFID tag, which isincorporated herein by reference. The self-tuning of the RFID tagensures optimal power transfer from the active device to the RFID tag sothat the RFID tag can use the received energy to transfer data back tothe active device. NFC passive devices are used in many applicationsbecause the passive NFC device can be a simple tag. NFC devicescommunicate with each other via radio waves. The active NFC device hasto be enabled (turned on) first. The radio waves for NFC are generatedusing an antenna. NFC works by exploiting the properties ofelectromagnetic fields, using the inductive coupling between NFCdevices. It operates at the 13.56 MHz frequency, which is a license-freesection of HF on the RF spectrum.

The strength of the received signal may be dependent on the distance aswell as external factors such as nearby objects, human touch, etc.Therefore, in some examples, RFID tags may include a switchablecapacitor bank that includes a plurality of capacitors coupled withswitches. The value of the capacitor may be changed by turning one ormore of these switches on or off. The input impedance of the receiverantenna may be changed by changing the capacitor value to optimize thesignal strength of the input signal.

In some RFID applications, such as tamper detection application or anyother application in which a stable ground is needed, some internalcircuits such as a limiter needs to be ground tolerant to make theoperations that depend on a stable ground possible.

FIG. 1 shows a schematic of an embodiment of an RFID tag 100 thatincludes an antenna port including pins to receive L_(A) and L_(B)inputs from an antenna. In some examples, the antenna port may beconfigured to receive signals via a wire coil type antenna. The RFID tag100, which may be incorporated in an integrated circuit (IC) and mayinclude a self-tuning circuit 102, an hybrid limiter 104, a modulator106 and a control logic 110. In some examples, the self-tuning circuit102 may be optional. The modulator 106 may be configured to encode theRFID tag interrogation request in a signal form and modulating thesignal and transfer the signal to the control logic 112. The controllogic 112 may include data that the control logic 110 may transmit backin the response to the interrogation request. The control logic 112 maybe configured for an application such as a tamper detection system. Arectifier 108 may be included to convert the signal between L_(A) andL_(B) into a DC signal which may be inputted to the control logic 112.Optionally, a DC limiter 110 may be included to limit the output DCvoltage level of the rectifier 108 to a preconfigured voltage level. Thehybrid limiter 104 is included to provide electrostatic discharge (ESD)protection and to limit the input signal voltage to a preconfiguredvoltage level to protect the downstream circuit in the RFID tag 100. Inone embodiment, as shown in FIG. 1 , the RFID tag 100 includes aninterface port 116 (e.g., I2C port) and a ground port 114.

Typical implementations of the limiter may include a transistor paircoupled between L_(A) and L_(B). While these implementations may beoptimized for the area on the silicon, these implementations do notprovide a ground tolerance that may be needed in some applications ofthe RFID tag 100. The typical implementations are susceptible to groundchanges that can be triggered by touching external interfaces (e.g. theinterface port 116). In case of such a ground change, the reference ofthe gate voltage V_(G) varies and this variation leads to a change inthe clamping voltage. Under certain conditions, like modulation, thechange in clamping voltage may lead to a loss of the function of theRFID tag 100.

FIG. 2 depicts the internal circuit of the hybrid limiter 104. Thehybrid limiter 104 limits both AC and DC voltages. The hybrid limiter104 includes transistors MN₁ and MN₂ coupled in parallel between L_(A)and L_(B). The gates of the transistors MN₁ and MN₂ are coupled togetherand are driven by a same gate voltage V_(G) that may be derived from theinput AC signal at L_(A)/L_(B). The transistors MN₁, MN₂ may be NMOStransistors in one example, to save the area on the silicon. Atransistor MN₃ is coupled between L_(A) and ground and a transistor MN₄is coupled between L_(B) and ground. In some examples, the hybridlimiter 104 may use a ground switch to implement a local groundconnection. An example implementation of a ground switch is disclosed byU.S. application Ser. No. 17/247,997 filed on Jan. 4, 2021 entitled“IMPROVED GROUND SWITCH”, which is described herein by reference.Transistors MN₃ and MN₄ may be of type NMOS and the transistors MN₃ andMN₄ are smaller in size compared to transistors MN₁ or MN₂. It should benoted that a PMOS transistor takes more space on the silicon, hencetransistors of type PMOS may not be suitable for the hybrid limiter 104.The physical size of the transistors MN₃ and MN₄ is kept smaller thanthe physical size of the transistor MN₁ so that transistors MN₃ and MN₄do not introduce substantial amount of parasitic capacitance. The gatesof the transistors MN₃ and MN₄ are coupled with the gates of thetransistors MN₁ and MN₂.

Transistors MN₁ and MN₂ limits or clamps the voltage between the twoantenna terminals L_(A) and L_(B). To prevent the impact of the shift inthe ground potential on the limiter function, transistors MN₃ and MN₄are included to generate ground reference for the transistors MN₁ andMN₂. The transistors MN₃ and MN₄ defines a local ground reference forthe hybrid limiter 104 only, hence, the power requirements for thetransistors MN₃ and MN₄ may be small, hence a smaller physical size ofthe transistors MN₃ and MN₄ may be used. The gates of the transistorsMN₁, MN₂, MN₃ and MN₄ are given by the gate voltage V_(G), which may beprovided by the logic control 114 in one example or may be derived fromthe output of the rectifier 108.

FIG. 3 shows an example of a tamper detection system that includes theRFID tag 100 and an antenna 120 coupled between the antenna terminalsL_(A)/L_(B). The RFID tag 100 may be affixed to a product 118 to detecta tampering. The product 118 may be coupled between the interface port116 and the ground port 114. The control logic 112 may be configured todetect ground on the interface port 116. If the link between theinterface port 116 or the ground port 114 and the product 118 is brokenor tampered with (e.g., if the product 118 is opened thus breaking thewire between the interface port 116 or the ground port 114 and theproduct 118). Upon detection of the tampering, the RFID tag 100 isconfigured to send a tamper indication to a RFID reader when the RFIDtag 100 is interrogated.

Some or all of these embodiments may be combined, some may be omittedaltogether, and additional process steps can be added while stillachieving the products described herein. Thus, the subject matterdescribed herein can be embodied in many different variations, and allsuch variations are contemplated to be within the scope of what isclaimed.

While one or more implementations have been described by way of exampleand in terms of the specific embodiments, it is to be understood thatone or more implementations are not limited to the disclosedembodiments. To the contrary, it is intended to cover variousmodifications and similar arrangements as would be apparent to thoseskilled in the art. Therefore, the scope of the appended claims shouldbe accorded the broadest interpretation so as to encompass all suchmodifications and similar arrangements.

The use of the terms “a” and “an” and “the” and similar referents in thecontext of describing the subject matter (particularly in the context ofthe following claims) are to be construed to cover both the singular andthe plural, unless otherwise indicated herein or clearly contradicted bycontext. Recitation of ranges of values herein are merely intended toserve as a shorthand method of referring individually to each separatevalue falling within the range, unless otherwise indicated herein, andeach separate value is incorporated into the specification as if it wereindividually recited herein. Furthermore, the foregoing description isfor the purpose of illustration only, and not for the purpose oflimitation, as the scope of protection sought is defined by the claimsas set forth hereinafter together with any equivalents thereof entitledto. The use of any and all examples, or exemplary language (e.g., “suchas”) provided herein, is intended merely to better illustrate thesubject matter and does not pose a limitation on the scope of thesubject matter unless otherwise claimed. The use of the term “based on”and other like phrases indicating a condition for bringing about aresult, both in the claims and in the written description, is notintended to foreclose any other conditions that bring about that result.No language in the specification should be construed as indicating anynon-claimed element as essential to the practice of the invention asclaimed.

Preferred embodiments are described herein known to the inventor forcarrying out the claimed subject matter. Of course, variations of thosepreferred embodiments will become apparent to those of ordinary skill inthe art upon reading the foregoing description. The inventor expectsskilled artisans to employ such variations as appropriate, and theinventor intends for the claimed subject matter to be practicedotherwise than as specifically described herein. Accordingly, thisclaimed subject matter includes all modifications and equivalents of thesubject matter recited in the claims appended hereto as permitted byapplicable law. Moreover, any combination of the above-describedelements in all possible variations thereof is encompassed unlessotherwise indicated herein or otherwise clearly contradicted by context.

What is claimed is:
 1. A Radio Frequency Identification (RFID) tag,comprising: an antenna port having first and second input terminals toreceive an input AC signal; and a hybrid limiter including a clampingdevice having a first transistor and a second transistor coupled inparallel between the first and second input terminals, the clampingdevice configured to limit a voltage of the input AC signal to apreconfigured limit, a third transistor coupled between the first inputterminal and a ground terminal, and a fourth transistor coupled betweenthe second input terminal and the ground terminal, wherein a gate ofeach of the first, second, third, and fourth transistors are coupledtogether to receive a gate voltage, wherein the third and fourthtransistors of the hybrid limiter are configured to provide a stableground reference for the first and second transistors of the clampingdevice.
 2. The RFID tag of claim 1, further including an interface portand a ground port.
 3. The RFID tag of claim 2, wherein the firsttransistor and the second transistor are of type NMOS.
 4. The RFID tagof claim 1, wherein the third transistor is smaller in physical sizethan the first transistor.
 5. The RFID tag of claim 1, wherein thefourth transistor is smaller in physical size than the secondtransistor.
 6. The RFID tag of claim 4, wherein a gate of the firsttransistor and a gate of the third transistor are driven by a same gatevoltage.
 7. The RFID tag of claim 5, wherein a gate of the firsttransistor and a gate of the fourth transistor are driven by a same gatevoltage.
 8. The RFID tag of claim 4, wherein the ground is coupled to aground switch.
 9. The RFID tag of claim 1, further including aself-tuning circuit coupled with the antenna port to optimize signalstrength of the input AC signal during a self-tuning phase.
 10. A tamperdetection system, comprising: a Radio Frequency Identification (RFID)tag, wherein the RFID tag includes an antenna port having first andsecond input terminals to receive an input AC signal and a hybridlimiter including a clamping device configured to limit a voltage of theinput AC signal voltage to a preconfigured limit, the clamping devicehaving a first transistor and a second transistor coupled in parallelbetween the first and second input terminals, a third transistor coupledbetween the first input terminal and a ground terminal, and a fourthtransistor coupled between the second input terminal and the groundterminal, wherein a gate of each of the first, second, third, and fourthtransistors are coupled together to receive a gate voltage, and whereinthe third and fourth transistors of the hybrid limiter are configured toprovide a stable ground reference for the first and second transistorsof the clamping device; an antenna coupled with the antenna port; aninterface port; and a ground port.
 11. The tamper detection system ofclaim 10, wherein the RFID tag is configured to detect tampering bysensing ground at the interface port.
 12. The tamper detection system ofclaim 11, wherein the RFID tag is configured to transmit an indicationof the tampering to an external reader when no ground is sensed at theinterface port.
 13. The tamper detection system of claim 12, furtherincluding a control logic configured to sense the ground at theinterface port and to transmit the indication to the external reader viathe antenna.
 14. The tamper detection system of claim 10, wherein theRFID tag further includes a self-tuning circuit coupled with the antennaport to optimize signal strength of the input AC signal during aself-tuning phase.